Controllers for touchscreen devices send the position-dependent signals generated by the touchscreens to analog to digital converters (ADCs) to be digitized before further processing is carried out to extract the positional information of interest. In cases where the devices are intended to be operated in environments with high RF noise, sophisticated digital filters may be applied to the ADC output signals. One example of a controller that uses this approach is the AMRI-5200 manufactured by Avago Technologies.
However, errors from the particular noise algorithms and cumulative arithmetic errors inherent to the use of digital filters may cause significant loss of precision in the filtered signal. To allow for this loss of precision, the ADC is designed to provide several more bits of signal precision at the filter input than are actually required at the filter output. Unfortunately, the use of a high precision ADC increases power consumption.
The issue of power consumption is particularly important for mobile consumer devices, as it has an obvious impact on battery life. However, it is reasonable to expect low to moderate RF noise in the mobile consumer device environment, except under extreme, infrequently occurring circumstances. The degree of digital filtering required in more typical circumstances is reduced, in turn requiring less precision in the ADC, and reducing power consumption.
What is needed is a touchscreen system, and method of operating such a system, that can switch between two modes, one for low noise situations, in which high ADC precision is not required, and one for high noise or other exceptional situations, when the power penalty associated with high ADC precision may be justified.